This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. There are several classes of naturally occurring catalytic RNAs or ribozymes. The importance of understanding how this class of biocatalysts promotes their reactions became evident with the recent structure determination of the 50S ribosome, which demonstrated that protein synthesis in all living organisms occurs within an RNA active site. Ribozymes are the molecules most likely to be the progenitors of modern biological catalysts and understanding how they promote their reactions provides critical insight into enzymological function. This project focuses on the structure of the group I self-splicing intron, the first class of catalytic RNAs discovered. Structural information is necessary to understand and interpret the biological function of this class of biocatalyst. We are working toward three goals. 1. The primary aim of this project is to determine the high resolution x-ray crystal structure of an intact bacterial group I self-splicing intron. If this aim is achieved, two additional projects will be undertaken: 2. Heavy metal ions and alternative intron inhibitors will be used to structurally investigate how metal ions contribute to group I intron folding and catalysis. 3. The transition state of the phosphotransfer reaction will be structurally explored using stable mimics of the transition state geometry. These studies will provide a structural basis for more than 20 years of biochemistry. It will also provide chemical insights into the nature of RNA catalysis, particularly for an RNA metalloenzyme, an example of which has not yet been structurally analyzed. RNA catalysis is an issue of particular interest given the critical of role of RNA in several natural processes including peptide bond formation and pre-mRNA splicing. The coordinates will be made available to the scientific community for analysis and experimental design.